Artificial gun shot effects



June 1956 J. L. HATHAWAY EI'AL 2,751,585

ARTIFICIAL GUN SHOT EFFECTS 3 Sheets-Sheet 2 Filed Jan. 12, 1953 &

June 19, 1956 J. L. HATHAWAY ETAL ,7

ARTIFICIAL GUN SHOT EFFECTS Filed Jan. 12, 1953 3 Sheets-Sheet 3 I' I F11 Y I I I I l l I I I I I I 2 I a an if! I I I I I I War! I {aw/=07 I 1 X912 ,ZJ/I 2 10 1 I I I I I I I I I I L; J I

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United States Patent ARTIFICIAL GUN SHOT EFFECTS Jarrett L. Hathaway, Manhasset, N. Y., and Raymond E.

Laiferty, Fairlawn, N. 1., assignors to Radio Corporation of America, a corporation of Delaware Application January 12, 1953, Serial No. 330,678

12 Claims. (Cl. 340-384) This invention relates to sound effects generating systems, and more particularly to systems for electrically generating a multitude of sounds representative of firearm discharges, waves crashing on a beach, roar of the wind and the like.

Apparatus in accordance with the invention is particularly applicable for use as a generator of sound effects for television or radio broadcasting studios and the like. Heretofore sound effects associated with the firing of guns and the like in both radio and television broadcasting have been uncertain and unrealistic. Moreover, certain effects are ditficult to obtain, for instance, machine gun fire and ricochet effects.

In broadcasting, recording, and the like, the sound effects representative of firearm discharges or explosions have generally been obtained by the firing of blank cartridges and with sound pick-up from a microphone. This method of obtaining sound effects has not been satisfactory in many respects as is obvious, and for the further reason that blank cartridges are not reliable. In some cases a cartridge may detonate with an ineffectual pop, and at other times, fail to detonate at all.

Another system extensively used for providing sound effects in broadcasting and the like is to reproduce from a recording of the actual sound or facsimile thereof, the particular sound effect desired. One disadvantage of this system is the problem of indexing the records, and placing of the phonograph stylus in the proper record groove at the proper time. In reference to firearm discharge, the transduction from sound energy to electrical energy and transmission through normal broadcast equipment does not produce a realistic report when converted back to sound energy because of the normal amplitude limitation of the transmitting and receiving equipment. In such a system Where the amplitude must be controlled to prevent overload, the high intensity sound of extremely short duration representative of a firearm discharge is heard, when reproduced, as a lower intensity sound of short duration. The apparent loudness of such a discharge may be increased by the persistence of a certain amount of reverberation, or increasing the duration of the lower intensity sound. However, in the case of television studios, the special acoustical treatment necessary to deaden the background noise results in lack of reverberation. This deadening efiect coupled with the amplitude restrictions'of the audio system is deleterious to realistic percussion reproduction.

It is accordingly an object of this invention, to provide a realistic and reliable sound effects system which effectively may utilize the output of a generator of random electrical signals in a predetermined manner.

Another object of this invention is to provide a sound effects system for certain sounds which has a signal channel including a generator of random electrical voltages,

.and means for controlling the amplitude pass characteristic of the system in relation to a predetermined time interval to simulate the wave envelope of the desired sound effect.

2,751,585 Patented June 19, 1956 Another object of this invention is to provide a system for electrically synthesizing and controlling random, electrical signals to produce reliable and realistic artificial gun shot effects and the like.

Another object of this inventionis to provide a sys-' tem for generating and controlling random electrical signals to produce reliable and realistic firearm discharge effects in a repetitive manner to simulate machine gun fire.

Another object of this invention is to provide a system for electrically generating sound effects simulating single or multiple firearms discharge followed by sounds of ricocheting bullets.

A further object of this invention is to generate realistic artificial gun shot effects which may be triggered by signals representative of actual firearm discharges to supplement and reinforce said signals in a program line for broadcast studios and the like.

In carrying out this invention in one form, it has been found desirable to provide a signal channel comprising a generator of random electrical signals or noise, and an amplifier for the noise signals. The signal channel may be connected with the program line of a broadcast studio. By selectively controlling the transmission characteristics of such a channel a multitude of sound effects may be synthesized.

For firearm discharges or other percussion sound effects, the signal channel is normally blocked. When it is desired to initiate the production of signals representative of firearm discharge, the signal channel may suddenly be unblocked to key on the noise signals as a sudden burst followed by a gradual decrease at a rate corresponding to the acoustical decay of the firearm discharge being simulated. If desired, special effects may be injected with the synthesized gun shot signals such as a signal from an oscillator whereby a ricocheting bullet is simulated, or the keying may be made repetitive so that the signals developed will simulate machine gun firing. The band pass frequency of the noise generator may be controlled to provide various gun shot efiects ranging from the crack of a small rifle to the boom of a distant cannon.

The keying or unblocking of the signal channel may be accomplished in different ways. It sufiices for radio or recording work that a button or other switch may be depressed or actuated to key the signal channel. -However, for television, Where the actor is frequently televised firing a gun, to achieve proper coordination between vision and sound, circuitry may be provided whereby the'signal channel may be keyed in response to signals representative of an actual gun shot. Thus the signals representative of an actual gun shot may be combined with, and reinforced by the synthesized gun shot signals.

Other sound effects may be obtained from the normally unblocked signal channel, for instance the roar of airplane engines, crash of surf on a beach, the roar of the wind and the like. These sound effects can be generated by controlling the frequency of the noise sig nals and selectively varying the transmission characten istics of the signal channel in such a manner to simulate the wave envelope of the desired sound. For example, if some of the high frequency components are eliminated and the transmission characteristics is set at a given level, signals simulating a fieet of bombers may be produced. If the gain of, the channel is advanced and then dropped rapidlwa signal simulating the building up and crash of waves on a beach may be produced. The transmission characteristics of the signal channel may be controlled in many ways, such as manually or by means of a cam arrangement. I

The random electrical signals from the noise generator may have wave lengths within the audio spectrum or within any higher frequency range. if the wavelengths are in a higher frequency range, a heterodyne oscillator may be used to beat with the noise signals to produce a band of noise signals having wavelengths within the audio spectrum.

Further features, objects and advantages will become 7 apparent from a consideration of the following description in conjunction with the accompanying drawings, in which:

Figure '1 is a simplified block and schematic circuit diagram of a sound'eflects generator for generating signals representative of firearm discharges;

Figure 2 is a block and schematic circuit diagram showing asystem for automatically keying a sound efiects generator in response to an actualgun shot whereby the signals'in the programline representative of the actual gun shot may be reinforced by the synthesized gun shot signals;

Figure .3 is a detailed schematic diagram showing a sound effects generator having circuits for generating signals representative of firearm discharges, discharges and ricochets, machine gun fire, and various degrees of each Figure 4 is a detailed schematic circuit diagram of an electronic gun shot generator having a system for auto- .matically keying the generator in response to a predetermined'high level signal from'the program line.

Referring now tothe drawings wherein like reference characters designate like components, Figure 1 shows a gun shot generator having a signal channel comprising a source of random electrical signals 30 coupled with an amplifier section including tubes 5, 7' which are connected in push-pull. Theoutput of the amplifier section may be coupled to the program line or other utilization means 17.

The source of random electrical signals or noise 3%) may be any of the several known types, but is has been found that the noise source of the variety as described hereinafter in connection with Figure 3, performs very well for the sound effects purposes to be described. The random electrical signals or noise may have wavelengths, substantially within the audio spectrum. However, it is possible to utilize noise with wavelengths within the higher frequency spectrums and to provide means for heterodyning the higher frequency signals with signals from a local oscillator to bringthe frequency range noise components within "the audio spectrum. The noise is coupled from the source 30 through a coupling transformer 31 to the grids "6, 8 of'the-push-pull amplifier tubes J7. If desired additional amplifiersmay be added to provide further amplification of the noise signals before these signals are fed to the push-pull'amp'lifiers 5,7.

'The amplifier "section including the tubes 5, 7 of the signal channel'is shown by way of example "aspush-pull, butother types of amplifier-s could be used as well. in the generation of gun shot signals the-signal channel is normally maintained blocked. This may be accomplished as shown in Figure 1 by maintaining the'amplifier tubes 5, 7 normally cut-off. A negative voltage from a bias source '15 may be connected through a resistor 12 and by way of a center tap 16 on the secondary of the coupling transformer 31 to the control grids 6, 8 of the amplifier tubes. The cathodes 18, 19 of the tubes are connected to a point of fixcdreference'potential or ground 14, through a cathode bias resistor 13 which supplies operating bias voltage when the tubes conduct.

One side of a'push button is connected to the center tap 16 'of the secondary winding of transformer 31, and the other side is 'connected'to thepoint offixedtreference potential or ground 14. Thus,'wh'en the push-button is The negative bias voltage is thereby removed from the grids "6, S'o'f'the amplifier tubes 5, '7 causing the tubes to 'conduet and amplify-the noise signals. Whenthe pushbutton 1'0'is released, the current from bias source begins to charge capacitor 11 which is connected "across the terminals of switch 10. Asthe condenser becomes charged, an "increasing "negative potential is applied 7 program line from the secondary of transformer 9, push I depressed, the center tap 16 is placediat.groundpotential.

button in is depressed to unblock the signal channel. During the time that the ,puSh-b'tttton It} is depressed, the tubes 5, '7 conduct as hereinbefore described, and the maximum amplification of the noise is effected. After the switch it} is released, the decaying'amplification simulates the efifect of reverberation. Thereproduced efiect of the sudden noise pulse with a relatively slower decay is essentially that of a gun shot. if the push-pull keyer tubes 5, 7 are purposely unbalanced to a slight degree, the D. C. tiuzmp component whichresults when the bias is suddenly removed, produces an impact with the shot to further enhance its realism.

in the production of signals representative .of firearm discharges it has been found that the acoustical energy within'the wave envelope is generally heterogeneous, and resembles noise. The ditie'rence inthc sound of gun-shots such as a pistol shot at close range and one at longer range is a function of the wave envelope of the shots or discharges and the frequency range of the signals Within the envelope. The envelopes of most shots have very steep fronts and trailing edges that decay relatively more slowly. By controlling the frequency-components present Within the wave envelopes, the sound efi'ects can 'be even more reliably reproduced. Thus the pistol shot at close range has a rapid attack followed by a gradual decay and the wave envelope includes many high frequency noise components. The pistol shot at longer ranges has a less rapid attack than the shot described above, and has a longer decay time due to reverberation efiects, and many of the high frequencies components'of the noise are attenuated by the air.

Ithas been foundthat the'most desirable-length of time for the switch'i'd to remain closed is from 6-16-1nilliseconds; For best results, the decay time after the switch in is opened 'is on the order of one quarter second and may be adjusted by proper selection of the values of resistor 12, and condenser 11 and the operating potentials 'applied'to't'he amplifier tubes 5,7.

"in general, manual operation of the switch it is un desirable because precise control of its closure period is necessary to produce reliable and realistic results. A method hereinafter described utilizes current responsive switches to control the hold-up period of switch it}. Other methods not using manual switches could undoubtedly be used to trigger the push-pull amplifiers 5,7. One such method might be the development of an unblocking voltage of apredetermined Waveform for direct application to grids 6, '8. However, for purposes of simplicity and understanding, the description will be limited to relay control switch 19.

Figure 2 shows a system for triggering the gun shot generator either manually or in response to an actual gun shot.

In the studio, sound transducing means such as microphone '21 is provided'to convert'soundsignals to electrical signals. These electrical signals from the'micr'ophone 21 are fed to an amplifier 22 for'amplification in a conventional manner. Amplifier 22-may include means for'comhitting-and controlling the outputs of other microphones not shown'herefor simplicity. The'output'from=amplifier on signals representative of firearmdischarges but is unaffected by screams, or shouts only a foot from the microphone.

The output from trigger circuit 23 in response to a high level signal may be a signal impulse and is shown in the drawings as connected across a relay energizing winding 28. The voltage pulse causes a current to flow in the relay winding 28 and a switch which is responsive to current flow in the winding 28 is thereby closed. The closure of switch 10 keys the normally blocked amplifier section as described with reference to Figure 1. The length of time that current flows through relay winding and hence the hold-up time of switch 10 may be controlled by proper choice of circuit constants in the trigger circuit 23.

If desired, the keying of the noise burst may be initiated manually by closing the contacts of switch 24. With switch 24 closed, a source of potential such as from battery 27 may be applied to condenser 26 through the relay winding 28. As the condenser 26 charges, energizing current will flow in relay winding 28 thereby causing switch 10 to close. The hold-up period of switch 10 in this instance depends on the value of the relay winding 28 inductance, the capacitance of capacitor 26 and the battery potential of battery 27. The closure of the switch 16 keys the random noise as previously described. A resistor 25 serves to discharge a condenser 26 after the contacts of switch 24 are opened.

For the purpose of firearm discharges the character of the noise voltage was found to have a bearing on the quality of the final reproduced result. Tests show that a smooth type of hiss gives the best results. Generators having spikes of high amplitude, even when followed by some degree of limiting in succeeding amplifiers, do not produce as good an effect as those having smooth, random electrical noise output.

Referring to the gun shot sound effects generator shown in Figure 3, the present equipment avoids the undesirable spikes by using an ordinary gaseous discharge tube 40 as a noise generator. This type of tube in combination with proper circuitry, is found to be non-critical and to develop a spike free noise voltage having frequencies substantially Within the audio spectrum. A load resistor 41 and a pair of direct current dropping resistors 42, 43 connect the anode of a gas tube 40 to a direct voltage supply lead 44-. The voltage supply lead 44 provides a positive potential which is only a few volts greater than necessary to cause and maintain conduction in the gaseous discharge tube and must be well filtered to avoid hum components in the noise voltage output. A pair of condensers 45, 46 respectively connect the junction of the resistors 41, 42, and 42, 43 to ground and serve as further filter elements to bypass audio frequencies including hum and noise components to ground. The cathode of gas tube 4%) may be directly connected to ground to complete the D; C. current path. A coupling condenser 47 couples the noise voltage output developed across load resistor 41 to the control grid of an amplifier tube 5%. Since the level of the output from the noise tube of the type shown is rather low, appreciable amplification should be provided before coupling with the program line. To this end amplifier tubes 50, 51 and 52 are connected to amplify the noise signal voltages in a conventional manner. The ouput of amplifier tube 52 may be fed through the coupling transformer 31 to the push-pull keyer tubes 5, 7 as shown and described in conjunction with Figure l.

The frequency band pass of the noise amplifier section may be controlled as shown 'in the grid circuit of am plifier tube 51. A grid leak resistor 61 'is connected by a conductor 60 to a wafer or a section-A-li'of a ganged switch. By changing the svitchpositions, circuit components are placed in shunt witlrthe grid leak resistor 61 whereby the frequency band pass may be selectively controlled.

When switch A-l is in any of positions B, C, E, ,F, J or K, resistor 62 and condenser 63 are both connected in shunt with grid leak resistor 61. With the switch in any of these positions there is provided a relatively wide band pass of frequencies in the audio spectrum including sufficient high frequency components of the noise signals to give the impression of light firearm discharges at several yards. In switch position D resistor 64 and condenser 65 are both connected in shunt to resistor 61. This RC combination is adjusted so the amplifier will pass an even wider band of audio frequencies including more of the high frequency components. At switch position G and H condensers 66 and 67 are respectively connected between the grid of the amplifier tube 51 to ground. These condensers bypass some of the high frequency components of the noise to ground so that for position G the noise components will have only the necessary quality to produce distant rifle etc. discharges or near cannon fire, and for position H the noise components passed will be predominantly the low frequency elernents having that quality for simulating distant cannon fire. In position L and I, condenser 86 is connected between the grid of tube 51 and ground to bypass enough of the high frequency components to ground to allow repetitive firing to sound like a pom-pom.

The operation of the push-pull keyer tubes (5, 7) is substantially the same as that described in Figure 1. However, in this embodiment the cathode circuit of one of the tubes 5, 7 may have additional variable resistance to selectively unbalance the operation of the tubes. As hereinbefore discussed, a slight unbalance will produce a D. C. thump component when the bias is suddenly removed to produce an impact with the shot to further enhance its realism. In the case of cannon fire where reduced impact is desirable (positions G and H of the ganged switch), push-button 79 provides switching contacts to short out unbalancing resistor 80.

The amplifier tubes 5, 7 of Figure 3 are held cut-off by a negative bias potential on a lead which is applied through one of the resistors 82 to 87 depending on the position of the wafer or section switch A-5, and through the secondary of transformer 31 to the grids 6, 8 of the tubes. A connection is made from one of the contacts 81 of a relay 90 to the center tap of the secondary of transformer 31, and the other of contacts 81 is connected through a small resistor 89 to ground. When the relay contacts 81 are closed in response to the energization of relay winding 90, the blocking bias is removed from the grids 6, 8. The RC time constant of the resistors selected at switch A-5 and the condenser 11 determines the length of time that the keyer tubes will conduct after contacts 81 have opened as discussed hereinbefore with reference to Figure l.

. For optimum conditions to produce reliable and consistently realistic gunshots, the keyer tubes should be allowed to conduct for maximum level for a selected predetermined time preferably from 6-16 milliseconds. As shown in Figure 3, the length of this time is determined by the hold-up period of contacts 81. It is the purpose of the circuitry connected with tube to automatically control this hold-up time, so that human errors, which would be present in manual switching, are eliminated. It is recognized that other systems might be used to unblock the keyer tubes and the description herein given is not meant to limit scope of the invention but rather to aid in understanding of this embodiment of the invention.

The operation of the device for single firearm discharges will be discussed first in which the ganged switch should be set to any positions, B, C, D, E, F, G, or H.

A vacuum tube 110, which is shown here as a triode, is normally maintained cut-.ofi by a negative bias potential from a lead 100 which is connected through a resistor 111,

.a pair of relay contacts 102 and 103 and another resistor to the grid of the tube 110. Relay winding 90 is connected in a space currentpath of the tube 110, and is energized thereby'to operate the relay contacts '101, 1102, 103, '81 and104.

Switch 120, which is represented here as a push-button, but may be any type of switch to make and break a circuit, is connected on one side to a source of positive potential through a lead 130 and on the other side through switch A2 and other circuitry hereinafter described to the grid of tube 110. When push-button 120 is depressed to close its contacts, currentfiows from positivesource of potential 130 through the closed switch 120, and resistors 114 and 112 to the negative biasing potential 100. The voltage developed by current flow through resistor 112 is also present across the series combination of condenser 113 and'resistor 111 which is connected in shunt with resistor 112. The condenser 113 charging current fiowing through resistor 111 will produce a voltage pulse thereacross. This pulse is taken fromthe junction of resistor 111 and condenser-V113 and is fed through contacts 102 and 10.3 and resistor 115 to the grid of tube 110. The pulse is of positive polarity with respect to ground and of sudicient amplitude to unblock tube 110 which then conducts to energize relay winding '90 thereby closing contacts 81, 1% and -'0112.

The negative potential from bias source 100 is now a-pplied directly to the grid of tube 110 through contacts 101 and 102 thereby blocking the tube. Since the relay winding is in the space current path of the tube 110, the relay'is energized to open contacts 81, 1G4 and 101- 102. Only one pulse is produced across resistor 111 so that when relay 9%) is deenergizcd, the negative biasing potential is applied to tube through resistor 111, contacts 102, 103, and resistor 115, and the normal cuton operation is resumed. No matter how long pushbutton is closed, only a single positive pulse will be produced to trigger tube 110.

Several systems might be used to repeatedly trigger the keyer tubes to simulate machine'gun fire, Such a system might have utilized a relay actuated by a low frequency oscillator, or the relay could have been made to vibrate at the desired rate either with or without a controlling vacuum tube.

For repetitive operation of this circuit to simulate the machine gun fire, the gang switch may be in one of the positions 1, K, I, or .L. in these switch positions the grid of tube 110 is connected throughtresistor 140, switch A 3, a second switch 2 1 and a condenser to ground. The grid is also connected through the resistor 115, relay contacts 102, 103 and resistor 111 to the negative bias potential lead 100 to maintain the tube 110 normally cut-01fv When push-button 120is operated, current flows from the positive potential lead through the push-button 120, resistors 116, 111, to the negative bias potential lead 100. The positive voltage developed by the current flow 7 through theresistors .116 and 111 taken from the junction point of these resistorsandis connected through the contacts 102, 103 to the .grid of tube 110 to unblock the tube. Tube 110 conducts to energize relay winding 90 thus closing ccntactsSl, 104 and 161102. The high negative potential .of lead 100'is then applied through contacts 101 and 102 to the tube 110. Depending .upon the position of switch S1 one of .the condensers 15.0 to 153 which maybe selectively connected in :the grid circuit of the tube 110 will be charged by this negative voltage through the small resistor 140.

When the ,high negative voltage cuts .off tubelidrelay winding 9.0 is deenergized andtcontacts .102, 103:are closed, and the positive voltage from the junction of .the resistor 116 and 111,'is again connected throughthe relay contacts and resistor 115 .to the grid 105. However, the tube is not unblocked immediately-as :the negative charge in theselected capacitor (.151 as shown), must leak ofi :through resistors 140, 115 and 1 11 and :the positive potential source 130 to ground. When the condenser '151 is sufficiently discharged, the tube-will conduct again repeating the cycle. The time "between theshots of the machine V 8 gunfire is thus dependent upon the time constant of capacitor 151 and resistors 140, 115, and 111. Bychanging the position of switch 5-1, a capacitor of difierent value is placed in the grid circuit of tube 110, and thus the time interval "between the shots can be varied.

Another efiect which is useful and desirable in gun shot sounds is shown in triodes and 180 which have a common cathode resistor 174. The plate load resistor 183 of triode'180 is much smaller than the plate load resistor 177 of triode 170. Thus the greater tube current in triode 180 causes a cathode bias voltage to be developed across the common cathode resistor 174 which is sufiicient to maintain triode 170 substantially cut-oil.

For operation of the ricochet and delay circuit, the ganged switch must be in one of the positions shown as B, C, D. When the push-button 120 is depressed, a positive voltage pulse is developed across the resistor 111 which triggers tube 110 as hereinbefore described. The same pulse is fed through an isolating resistor 172, a condenser 171, and a switch -A-4 to the grid 173 of the tube 170. This positive pulse unblocks triode 170 and causes conduction therein, thereby reducing the plate voltage of that tube so that a negative voltage pulse is fed through condenser 176 to the tube 180, cutting it off. The delay time from the start of the synthesized shot to the start of the ricochet oscillations is equal to the time tube 180 remains cut-off and is a function of the RC time constant of condenser 176 and variable resistor 175. Resistor may be preset or may be brought out as a front panel control to selectively vary the ricochet delay time. When capacitor 17.6 discharges sufiiciently through resistors 175, 178, and 1.74, to bring the grid of tube into the conduction region, the cycle is completed and tube 180 is snapped into heavy conduction. By virtue of the interconnection of the cathodesas previously described, triode 170 is returned to cut-off.

Relay tube 160normallyconducts to maintain energized a relay winding 161 which is connected in the space cur rent path of the relay tube. When tube 130 snaps back into conduction, a large voltage surge appears in the plate circuit of that tubev This surge is ditierentiated through a condenser 181 and a resistor 182 to produce a negative pulse atithe grid of the relay tube 160. The relay tube then amplifies the negative pulse toeilect a momentary deenergization of the relay winding 151.

The relay winding 161 controls a pair of contacts, 162 which are connected in the grid circuit of tube of the ricochet tone multivibrator. The tone multivibrator cornrises tubes .190 and 200. Tube 190 is normally cut-off by the high negative bias voltage from lead 100, which is connected to its grid through resistors 196, 197 and 19,3. Tube 208 normally conducts by virtue of the high positive voltage from lead 205 which is connected to its grid through resistor 201. When the relay 161 is momentarily deenergized to close its contacts 162, a condenser 191, which is connected in .the grid circuit of the tube 190, is charged by a positive voltage from lead 195. The positive voltage across the condenser 191 is presented to the grid of tube 1% and causes that tube to conduct. The tube conduction causes a drop in plate voltage, and a negative pulse is thus delivered through switch A-6,

and through one of the condensers 202, 203, 204 to the grid'of tube 200. This negative pulse cuts on tube 200 for a period-of time :depending on the RC dime constant of the condenser selected and resistor 201. As :soon :as

greases the charge leaks off the selected condenser sufiiciently, tube 200 snaps back to conduction, and a negative pulse is delivered through condenser 192 to the grid of tube 190 driving it into cut-01f again. The period of cut-off of tube 190 depends on the RC time constant of the condenser 192 and the resistor 197, and the potential across the condenser 191. When condenser 192 discharges sufliciently, the positive voltage from condenser 191 will cause 1% to conduct again, thus repeating the cycle. The cycle is designed to continue at an audio rate.

As has been stated the condensers 202, 293, 204 may be selectively connected into the circuit through switch A-6, thus allowing control of the initial frequency of oscillation. However, to make a realistic ricochet the tone must fall E because of down doppler, and the sound should fade away. To accomplish this, a resistor 106 is connected to serve as a discharge path for condenser 191, so that the positive voltage delivered to the grid of tube 190 gradually decreases, and thus the frequency of operation and the amplitude of output of the ricochet multivibrator are decreased. The output from the ricochet multivibrator is fed from the grid circuit of the tube 260 through a condenser 55 to the cathode circuit of the amplifier tube 52 of the noise amplifier section. Because the ricochet oscillator continues to function until the voltage as condenser 191 drops below ground potential, a means is provided to quickly discharge this capacitor to permit other ricochet shots to follow in rapid sequence. Otherwise, during the delay period between the second shot and its ricochet, low pitched oscillations remaining from the previous shot would be heard. The pair of open contacts 104 on the triggering relay 90 are therefore connected across this capacitor so that each time a shot is fired contacts 104 close to quickly discharge condenser 191.

Each time that push-button 120 is depressed and relay 9!? is momentarily actuated to close the contacts 81 the keyer tubes are unblocked momentarily. The output of these tubes is fed through transformer 9 to the program line. In order to permit head set monitoring or last minute selection and adjustments, a phone jack 210 is provided which disconnects both the shown output channels. Thus, the control settings, as well as overall performance, may be checked during a show. Output level may be adjusted by means of an indicator such as a neon tube 211 if necessary.

Figure 4 is a schematic diagram of a circuit for automatically triggering the keyer tubes in response to signals from an actual gun shot. The program input is connected to terminals 230 and 231, and fed through a transformer 232 to a pair of tubes 240, 250 connected in conventional push-pull relation. The output of these amplifier tubes may be taken from the output terminals 251, 252 on the secondary winding of transformer 241.

Block I includes the noise generator and amplifier which feeds the noise signals to keyer tubes shown in block II and which was hereinbefore described in reference to Figure 3. Block V represents a power supply which may be used for operation with this circuit.

The keyer tubes of block II are triggered into operation by the trigger circuit shown inblock III which is in turn actuated by signals of predetermined high level representative of actual gun shots. A trigger relay winding 261 is connected in the space current path of the trigger tube 260 and the contacts controlled thereby constitute a switching arrangement connected with the grids of the keyer tubes. A cathode resistor 263 and a resistor 264 are connected between ground and a source of positive potential and form a voltage divider network. The triggertube is normally maintained cut-oft by virtue of the bias potential developed across the cathode resistor 263.

The grid of the trigger tube 260 is connected to ground through a resistor 262. When voltage is developed across the grid resistor 262 which is of suificient amplitude, tube 261' is driven out of cut-off and relay 261 is energized.

A rectifier 265 is connected from one end of the secondary winding of the signal input transformer 232, to a source of positive operating potential 270 through the resistor 267, 266. A coupling condenser 268 connects the junction of resistors 266, 267 to the grid of trigger tube 269. When the incoming signal level reaches a predetermined high level representative of the level of gun shot signals, the rectifier 265 will become conductive causing current to flow in resistor 266, 265.

This current flow produces a voltage change or pulse at the junction of the resistors 266, 267 which is integrated across the RC combination of the grid resistor 262 and the coupling capacitor 268, to produce a voltage pulse across the grid resistor 262 of such polarity and magnitude to unblock trigger tube 260. When the tube 260 conducts, the relay winding 261 is energized to close the relay contacts. The relay contacts connect the grids of keyer tubes 5, 7 to ground through a small resistor thereby removing the blocking bias. In this manner the keyer tubes are actuated in response to high level signals to produce synthetic signals representative of gun shots.

In the operation of the device as shown in Figure 4, high level signals representative of an actual gun shot are fed together with the regular program signals to the amplifier section shown in block IV.

The trigger circuit is coupled to the input of the amplifier section and is so designed that it is responsive to signals over a predetermined amplitude, such as the actual shot signals. A signal of such character causes the tube 16% to conduct as described thereby energizing the relay winding 261 whereby the relay contacts are closed.

Upon closure of the relay contacts the keyer tubes shown in block II conduct and a signal representative of a gun shot is developed and fed to the grid circuit pushpull of the amplifiers 240, 250. The signals representative of an actual gun shot are thereby reinforced by the synthesized signals, and the composite output may be obtained from the output terminals 251, 252 of the amplifier section. Tests indicate that hand-clapping, shouts, and screams within six inches of the microphone will not trigger a device constructed in accordance with Figure 4, but gun shots will operate the circuit satisfactorily.

While exemplifications of the invention have been indicated and described above, it will be apparent to those skilled in the art that other modifications may be made without departing from the scope of the invention as set forth in the appended claims.

What is claimed is:

1. In a sound effects system for electrically generating signals representative of firearms discharge, a signal conveying channel comprising a generator of random electrical voltages, an amplifier for said voltages connected with the generator, transducing means for converting electrical energy to sound energy connected with said amplifier, a first control means connected with said amplifier to maintain said amplifier blocked, and a further control means connected with said amplifier for momentariiy rendering said amplifier unblocked in time duration and amplitude such that random electrical voltages from said generator are passed through said system to said transducer in an envelope which simulates signals representative of said firearms discharge. 1

2. A percussion sound effects system comprising a signal generator for providing noise voltages, an amplifier for said voltages including at least one electron tube having an anode, a grid and a cathode, an output circuit connected with said anode and cathode, a source of blocking bias potential connected with the grid and cathode of said tube to maintain said tube substantially cut-off, circuit means including a switch device and a capacitor connected between said grid and a point or reference potential to render said tube conductive in response to momentary actuation of said switch whereby said noise voltages are amplified to produce a signal in said output circuit, said capacitor having a value and being controlled in therewith such that inresponse to actuation of said second switch current flows in said circuit for a predetermined length of time, thereby actuating said current responsive switch device for apredetermined length of time.

7 4. In a systemfor producing percussion sound efiects, a signal channel comprising a generator of random elec trical voltagespan implificr for said voltages, an output circuit connected with said amplifier, a first means to maintain said system normally'blocked, further means for 'unbloclting said system for a predetermined length of timeya second signal channel, a trigger circuit connected with said second signal channel, said trigger circuit being responsive to higlrlevel signals representative of actual gun shots, said trigger circuit further being connected with said unblocking means such that said signal channel is unblocked in response to actuation of said trigger circuit, whereby said random electrical voltages are passed having a Waveform simulating the waveform of signals representative of firearms discharge.

5. A system for producing gun shot sound efiects, comprising a generator providing noise voltages which have wave lengths substantially within the audio frequency spectrum, an amplifier for said voltages including a first electron tube having an anode, a grid, and a cathode, transducing means for converting electrical energy to sound energy connected with said amplifier, a source of biasing potential coupled with the grid and cathode of said first tube to maintain said amplifier blocked, means including a current responsive switch for removing said biasing means from the grid and cathode of said first tube amplifier for a predetermined length of time whereby said amplifier is rendered conductive, means for controlling said current responsive switch including a second electron tube, said switch being responsive to the space current flow of said second tube, means including a manually operated switch for changing the state of conductivity of said second tube for a predetermined length of time, whereby said current responsive switch is actuated, further circuit means including a resistor and a condenser connected with said first tube and operable after said predetermined time to gradually reduce the conductivity of said first tube to cut-off, whereby said sound energy from said transducing means rises sharply to a high level for said predetermined length of time, and decays to'a lower level during a relatively longer period of time.

6. A system for producing machine gun shot sound effects comprising an electrical generator of random noise voltages, an amplifier and said voltages, transducing means for converting electrical signals corresponding to said voltages to sound signals connected with the generator through said amplifier, control means for said amplifier including a source of biasing potential connected with said amplifier for normally maintaining said amplifier blocked to restrict the flow of said voltages therethrough, circuit means including a switch device and a capacitor connected to render said control means inoperative for a predetermined time interval thereby to render said amplifier conductive at a high level over said time intervals, means for momentarily actuating said switch device at successively spaced intervals of time, and further control means for said amplifier including a resistor and a capaci tor connected with said amplifier and operable after each of said predetermined time intervals to gradually reduce the conductivity of said amplifier to cut-off whereby sound signals -which have risen sharply to relatively high levels for each :of said time intervals are caused to decay during relatively long periods of time to a lower level.

7. A sound effects system for generating firearm discharges followed by ricocheting' sounds including an electrical generator of'random electrical voltages, an amplifier for said voltages, transducing means connected with the generator through said amplifier for converting electrical signals corresponding to said voltages to sound signals, control means for rendering said system conductive to supply said voltages to operate said transducer for a predetermined time interval, additional control means in said system and connected between said generator and tranducer for modifying said voltage whereby the sound level produced by said transducing means rises sharply near the beginning ofsaid interval and subsequently decays at a relatively slower rate, audio'oscillator means connected with said amplifier, and means to delay the application of oscillations from said oscillator to said amplifier for a predetermined time after said system is rendered conductive.

8. A sound effects system'for generating firearm dischargesas defined in claim 7 wherein the means to delay the application of oscillations from said oscillator to said amplifier include a single shot multivibrator.

V 9. A sound effects system for generating firearm discharges as defined in claim 7 wherein said audio oscillator has means for changing the frequency of oscillations thereof including a capacitor provided with a discharge circuit connected with said audio oscillator whereby the potential across said capacitor controls the frequency of said oscillations, a source of potential for normally charging said capacitor and means for removing said source of charging potential during said predetermined time interval whereby the charge on said capacitor may gradually leak away.

10. A system for reinforcing and supplementing electrical signals representative of gun shot sounds, comprising a first signal-channel including input and output circuits, means for transducing sound'energy from actual shot sounds to electricals'ignals connected with said input circuit, and sound energy reproducing means connected with said output circuit; a second signal channel having input and output circuits for generating synthetic gun shot signals comprising a generator of random electrical voltages connected with saidinput circuit, control means connected with the second channel for rendering the channel conductive to pass said random electrical voltages from said generator therethrough for a predetermined time interval, and additional control means in circuit with said second channel for controlling the amplitudepass characteristic of the system in relation to said time interval to simulate a wave envelope of a gun shot; means responsive to signals of a predetermined high level connectcd with said first signal channel for actuating the control means connected with .said second channel whereby said second channel is rendered operative by said high level signals, and means connecting the output circuit of said second signal channel with said first signal channel, whereby the signals representative of the actual gun shot sounds are reinforced and supplemented by the controlled random electrical signals.

11. In a system for generating signals representative of gun shot sound effects and reinforcing signals representative of actual gun shot sounds, a first signal channel comprising means for transducing sound energy from actual shot sounds to electrical energy, an amplifier for said electrical energy connected with said first named means, and sound energy reproducing means connected with said amplifier; a generator of synthetic gun shot signals comprising a source of noise voltages, an amplifier for said noise voltages, an output circuit for said amplifier, control means 'for normally maintaining said noise voltage amplifier cut-off and further means for rendering said noise voltage amplifier conductive for a prodeterrnined length of time and additional control means in said system connected between said generator and transducer for modifying said voltages whereby said noise voltages are amplified by said noise voltage amplifier such that a signal having a wave envelope representative of gun shot signals is produced in said output circuit, a trigger circuit having output terminals and responsive to signals of a predetermined high level connected with said first named amplifier, means connecting the output terminals of said trigger circuit with said means for rendering said amplifier conductive whereby the noise amplifier is unblocked in response to activation of said trigger circuit; and means for connecting said output circuit of the noise voltage amplifier with said first mentioned amplifier, whereby the signals representative of the actual gun shot sounds are reinforced by the synthetically generated signals.

12. In a system for generating signals representative of gun shot sound effects and reinforcing signals representative of actual gun shot sounds; a first signal channel comprising means for transducing sound energy from actual shot sounds to electrical energy, an amplifier for said electrical energy connected with said transducing means, and sound energy reproducing means connected with said amplifier; a generator of synthetic gun shot signals comprising a source of noise voltages, an amplifier for said noise voltages having an input circuit and an output circuit, a source of biasing potential connected with the input circuit of said noise amplifier to normally maintain said amplifier blocked, means including a current responsive switch connected between said input circuit and a point of reference potential, said amplifier being unblocked for a predetermined time interval in response to the activation of said switches, further means including a resistor and a capacitor connected with said input circuit and operable during said time interval to gradually reduce the conductivity of said amplifier to cut-off whereby sound signals which rise sharply to a relatively high level decay to a lower level during a relatively longer time thereafter; a trigger circuit including an electron tube responsive to signals of a predetermined high level, said trigger circuit being connected with said first named amplifier whereby the state of conductivity of said electron tube is controlled by high level signals in said amplifier, said current responsive switch being responsive to the current flow in said tube whereby change in the state of conductivity of said tube operates said switch to un block the noise amplifier; and means for connecting said output circuit of the noise voltage amplifier with said first mentioned amplifier, whereby the signals representative of the actual gun shot sounds are reinforced by the synthetically generated signals.

References Cited in the file of this patent UNITED STATES PATENTS 2,455,472 (Burl et a1. Dec. 7, 1948 2,483,226 Newman Sept. 27, 1949 2,500,063 Crane Mar. 7, i950 

